Foam Core Sandwich Research Articles

On low-velocity impact response of metal foam core sandwich beam: A dual beam model

A theoretical procedure for dynamic response of metal foam core sandwich beams struck by a heavy mass with low-velocity is developed to consider the combined local denting and global deformation. Analysis focuses on effect of local denting on global deformation and inertial effect of the structure. Large deflection effects are determined by using the membrane factor method. A set of finite element simulations is carried out to validate the model predictions. It is demonstrated that the model predictions are in good agreement with the finite element computations. The sandwich beam is strengthened with the deflection increasing.

Influence of core joints in sandwich composites under in-plane static and fatigue loads

Most designers are unaware of the influence of core junction in lightweight sandwich structures under axial load. Quantifying this effect and its criticality on the life of the structure is still a challenging task. In this study, a novel testing methodology was used to characterize this effect. Scarf and butt core joints in foam core sandwich composites were subjected to axial static and fatigue loads (R=0.1 and R=−1). Under cyclic axial load, differential movement (through-the-thickness) between the foam and core joint was more significant than anticipated. Non-destructive evaluation techniques were used to locate the damage and assess the failure mechanisms. The root-cause-failure analysis showed that cracks were initiated in the facesheets for the butt-joint, and in the core for the scarf-joint samples, respectively. Consequently, at 80% residual strength, the butt-joint reduced the predicted fatigue life by 42% and 32% at low and high cycle fatigue, respectively. Residual tensile tests revealed the sizeable damage induced by the traditional butt-joint design. This research confirmed that despite the facesheets' primary in-plane load carrying mechanisms, core junction will substantially influence the axial fatigue life of the structure.

Experimental and numerical study of aluminum foam-cored sandwich tubes subjected to internal air blast

Abstract The blast response of aluminum foam-cored sandwich tubes that were subjected to internal air blast was investigated experimentally and numerically. Blast experiments were performed to capture the fundamental deformation, the maximum deflection of the inner face-sheet (MDIF), and the maximum deflection of the outer face-sheet (MDOF). A special MDOF (SMDOF) can be achieved by normalizing the MDOF with respect to the corresponding face-sheet radius and tube mass. Results confirm that the SMDOF of sandwich tubes is moderately sensitive to the core relative density, internal diameter, core thickness, and explosive charge. The finite element (FE) model was constructed using the Voronoi algorithm. After verifying the FE model, numerical studies were conducted to investigate the deformation process of sandwich tubes, the densification of double-layer cores, and the effects of core arrangement and face-sheet thickness on blast resistance. The SMDOF is influenced by the inner and outer face-sheets, whereas the special energy absorption (SEA) is mainly affected by the inner face-sheet.

Experimental study on stress attenuation in aluminum foam core sandwich panels in high-velocity impact

The present work examined the dynamic behaviors of sandwich panels with aluminum foam core and steel faceplates at an impact velocity of about 370m/s. The stress attenuation before and after the foam core during penetration process was measured by means of Polyvinylidene Fluoride transducers. It was found that the stress value was remarkably reduced, and the rise velocity of stress slowed down evidently as foam core was compressed. The profile of the damaged aluminum foam illustrated no obvious localized “X” failure patterns at the velocity tested presently.

Quasi-static and dynamic compression behavior of glass cenospheres/5A03 syntactic foam and its sandwich structure

5A03 aluminum matrix syntactic foam filled with glass cenospheres was synthesized using pressure infiltration technique. This paper focused on the compression behavior of syntactic foam at quasi-static (10−3s−1) and dynamic (strain rate 1×103s−1–3×103s−1) condition, and the dynamic response of syntactic foam core sandwich structure with two different wave impedance front-panels (A3 steel and AZ31) subjected to split-Hopkinson pressure bar. The syntactic foam at dynamic loading exhibited a maximum 43% increase in peak strength, 38% in plateau strength, and 23% in energy absorption capacity compared to quasi-static results, with 0.03 strain rate sensitivity similar to that of aluminum matrix. The dynamic compression behavior can be concluded as thin near-45° shear bands forming, deformed area propagating to the central and lateral parts, and finally densifying with significant lateral expansion. The sandwich structure exhibited great energy absorption capability due to the syntactic foam core. The higher wave impedance front-panel would be conducive to the energy absorption capability of syntactic foam core into full play.

Three-dimensional solution of low-velocity impact on sandwich panels with hybrid nanocomposite face sheets

ABSTRACTIn this article, a three-dimensional solution based on Fourier's series and the generalized differential quadrature method is presented to model the low-velocity impact on sandwich panels with hybrid nanocomposite face sheets. Navier's equations are derived and displacements are substituted by their corresponding Fourier's series. The contact force is considered as a Fourier's series of impactor displacement and deflection of contact point. To verify the theoretical model, experiments are performed on a polyurethane foam-cored sandwich panel with epoxy/woven-fiberglass/nanosilica hybrid nanocomposite face sheets. Contact force and lateral displacement of contact point histories are compared with the theoretical model.

Aromatic thermosetting copolyester foam core and aluminum foam face three-layer sandwich composite for impact energy absorption

In this work, we introduce a three-layer sandwich composite structure having an aromatic thermosetting copolyester (ATSP) foam core with two aluminum foam face layers joined together by an in situ generated foaming mechanism. The ATSP foam core was synthesized on-site between the aluminum foam layers via a heat-induced polycondensation reaction. Upon curing, the ATSP foam core adhered to the aluminum foam layers through an interfacial compatibility-enabled chemical bonding. Lap shear experiments demonstrated that the bond strength clearly surpassed the tensile performance of the bare aluminum foam parts. Drop-weight impact tests showed that the three-layer sandwich structure could absorb four times the impact energy as compared to the bare aluminum foam of the same overall thickness.

Investigation of elastomeric foam response applied as core for composite sandwich beams through progressive failure of the beams

In this paper an elastomeric foam is applied as core for the composite sandwich beams and load carrying capacity, load–deflection response, and progressive failure are examined through experimental and finite element studies. The objective of this study is to assess the efficiency of elastomeric foam-cored sandwich (EFCS) beams relative to crushable foam-cored sandwich (CFCS) beams. The experimental program consists of two phases. In the first phase, some characterization tests are conducted on the constituent materials of the sandwich beams such as tension, compression, and shear tests on the foam and bending test on the composite beams utilized as skins. Then in the second phase, the performance of the sandwich beams is examined under bending conditions. The load carrying behavior of the sandwich beams is considered dependent on two main features of the constituent materials: (1) the hyperelastic behavior of the foam core and (2) the progressive damage of the composite skins. These characteristics are simulated by the finite element models. Due to elastomeric rather than crushable deformation of the applied foam as the core, the conventional damage modes of the CFCS beams associated to the brittleness of the core material are omitted through load carrying capacity of the EFCS beams. So in the recent sandwich beams by omission of the core failure modes and utilization of compressive residual strength of the top composite skin, considerable energy is absorbed prior to failure of the bottom composite skin. By simulation of the test specimens using FE models, the response of the foam applied as core for the sandwich beams through progressive failure of the beams is investigated. The results show that the elastomeric foam core can provide superior features for the sandwich components especially for the cases in which high energy absorption capacity is required.

Mode I interfacial fracture characterization of foam core sandwich materials at elevated temperatures

Foam core sandwich materials are being widely used in structural engineering due to their advantages such as lightweight, high strength, and corrosion resistance. But the interfacial bond strength of foam core sandwich materials is weakened at elevated temperatures. In practice, the influence of high temperature cannot be ignored since the composites with foam are sensitive to the change in the environment. In this study, a series of sandwich double cantilever beams were tested at different temperatures to evaluate the effect of high temperatures on the interfacial fracture of the foam core sandwich materials. The temperature range studied was from 30 to 90℃, noting the glass transition temperatures are 85.7℃ for the composites and 72.1℃ for the foam core, respectively. In the meantime, the mode I interfacial crack propagation and its corresponding interfacial strain energy release rate were analyzed. Furthermore, an analytical model, considering the change in temperature, was proposed to predict the strain energy release rate of mode I interfacial facture of the foam core sandwich materials. The analytical results were found to be well matched with the experimental results.

Perforation resistance of sandwich panels with layered gradient metallic foam cores

The perforation resistance capability of clamped square sandwich panels with layered gradient metallic foam cores subjected to the hemispherical-nosed projectile impact was investigated numerically. The previous penetration tests on monolithic foam core sandwich panels were used to validate the present simulation approach, and then the deformation process, critical velocity and energy absorption of monolithic Al plate, ungraded and layered-gradient sandwich targets were studied, respectively. Influences of the strain rate and asymmetric face-sheets on the perforation resistance of the layered-gradient sandwich target were also discussed. The simulation results indicate that layered-gradient sandwich targets have the worst perforation resistance and energy absorption capability, and then the ungraded sandwich panel, and the monolithic plate is the best. For layered-gradient sandwich panels, the perforation resistance is hard to improve obviously by changing the arrangements of core-layers. Besides, the strain rate effect of materials and asymmetric face-sheets contribute to enhance the perforation resistance of layered-gradient sandwich targets only for the low-velocity penetration condition. These findings are beneficial for guiding the design and assessment of layered-gradient sandwich structures in engineering applications.

Interfacial crack arrest in sandwich beams subjected to fatigue loading using a novel crack arresting device – Numerical modelling

A novel crack arresting device is implemented in foam-cored composite sandwich beams and tested using the Sandwich Tear Test (STT) configuration. A finite element model of the setup is developed, and the predictions are correlated with observations and results from a recently conducted experimental fatigue test study. Based on a linear elastic fracture mechanics approach, the developed FE model is utilised to simulate crack propagation and arrest in foam-cored sandwich beam specimens subjected to fatigue loading conditions. The effect of the crack arresters on the fatigue life is analysed, and the predictive results are subsequently compared with the observations from the previously conducted fatigue tests. The FE model predicts the energy release rate and the mode mixity based on the derived crack surface displacements, utilising algorithms for the prediction of accelerated fatigue crack growth as well as the strain field evolution in the vicinity of the crack tip on the surface of the sandwich specimens. It is further shown that the developed finite element analysis methodology can be used to gain a deeper insight onto the physics and behavioural characteristics of the novel peel stopper concept, as well as a design tool that can be used for the implementation of crack arresting devises in engineering applications of sandwich components and structures.

Numerical study of energy absorption in aluminum foam sandwich panel structures using drop hammer test

The sandwich structures with aluminum foam core and metal surfaces have widespread use in the absorption of energy, because they are light weighted with high performance in dissipating energy. The cell structure of the foam core is subjected to plastic deformation in the constant compression level that absorbs a lot of kinetic energy before destruction of the structure. In this research, experimental tests of low-velocity impact on the sandwich structure by a drop machine are simulated by LS-DYNA software. Numerical results are obtained for different velocities and weights of projectile on samples of aluminum foam core sandwich panels with relative density (the ratio of the density of aluminum foam to the density of solid aluminum) of 18, 23, and 27. The results are compared with experimental results which reveal a good conformity. As well, from the numerical simulations, the effect of weight, velocity and energy of the projectile and the density of the foam core on the global deformation and energy loss rate of projectile have been studied.

Influence of hygrothermal conditioning on strength and stiffness of rigid foam core glass/epoxy skin sandwich composites

An experimental study was conducted to evaluate the hygrothermal effects on the rigid polymer foam core sandwich composites at a given temperature and humidity conditions. Fabrication of the poly-urethane or poly iso-cyanurate core based, glass/ epoxy face sheet based sandwich composites of 65 Kg/m3 and 251 Kg/m3 foam densities by hand layup followed by vacuum bagging technique, are discussed. The panels were sliced and honed according to the required dimensions for a span to depth ratio of 16:1. The specimens were then maintained at 40°C and 90% relative humidity conditions in a hygrothermal chamber for days till saturation equillibrium. Three-point bending tests were performed for hygrothermally saturated specimens and unconditioned specimens. Finally, a comparison of the test results of the saturated and unconditioned specimens was made. The moisture saturated specimens show lower strength and stiffness than unconditioned specimens, in addition to a few more results. A discussion is provided on the absorption models for moisture at elevated temperatures and their influence on the property degradation.

Shear Flow Analysis in Foam Core-Glass/ Epoxy Face sheet Sandwich Composites

Studies on understanding the shear flow by varying geometry and skin to core weight ratios of sandwich composites help identify the failure patterns and correlate them with the observed test data. Glass/epoxy skin- rigid foam core sandwich composites used in niche applications exhibit various types of failures under static loading conditions. The current study focuses on understanding the shear flow patterns in core failure by flexure. Polyurethane and Polyisocyanuraterigidfoams of 65 kg/m3 and 126kg/m3 densities were considered for the study.Sandwich panels with glass fabric/ epoxy skin were fabricated by maintaining different skin to core weight ratios with various core thicknesses of 10mm, 25mm and 50mm.. Tensile and compressive data evaluated analytically were used to determine the shift in neutral axis for the flexural specimens by finding the ‘r’ (shift) ratio. The influence of the shift on the shear flow patterns were observed in each case and presented.

Design of Active Frequency Selective Surface with Curved Composite Structures and Tunable Frequency Response

We present an active frequency selective surface (AFSS) consisting of a curved composite structure that provides structural stability and robustness. The proposed structure can operate on either the C-band (OFF state) or X-band (ON state) by controlling the PIN diode located between the cross-shaped loop and the inductive stub on the surface. Moreover, it minimizes parasitic couplings through grid-type on/off bias circuits and via holes. Thus, the AFSS guarantees isolation from the unit cell, which is a downside of a previous control technique called reconfigurable frequency selective surface. We analyzed the impact of composite structures and the three-dimensional shape on the AFSS transmission with a foam-core sandwich structure, which is light and mechanically strong, by considering conditions of a real application environment.

Low velocity bending impact behavior of foam core sandwich beams: Experimental

Abstract This experimental study addresses the low velocity impact bending response of sandwich beams with expanded polystyrene (EPS) foam core reinforced by aluminum face-sheets using adhesive bonding technique. The deformation behaviour and the effects of the geometric and mechanical design parameters were investigated to improve the impact energy absorbing capability. The bending impact tests were performed for different foam density, foam and plate thicknesses for three impact energy levels: 4.45 13.05, 26.78 J. The photographs of the permanent deformation geometries of the sandwich beams were presented and the contact force and kinetic energy histories were discussed. The specimens with higher foam core density and thicker foam core resulted in the lowest permanent central deflections and contact force variations. As the foam core density and thickness were increased, the energy absorbing capability was improved. The specimens having thinner face-sheets exhibited higher contact force variations and the lower permanent deflection than those of the specimens with thicker face-sheet even for the lowest impact energy. However, as the impact energy was increased, the specimen with thinner face-sheet exhibited lower contact force levels and higher permanent deflections than those of the specimens having thicker face-sheets. In addition, the plastic dissipation energy was increased in the face-sheets. The face-sheet thickness was more effective on the permanent deflections, whereas the foam core density was more effective on the energy absorbing capability.

Theoretical model of low-velocity impact on foam-core sandwich panels using finite difference method

In this article, a three-dimensional solution based on the Fourier’s series and finite difference method has been presented to study the low-velocity impact on sandwich panels with foam core and composite face sheets. The Navier’s equations are derived and displacements are substituted by their corresponding Fourier’s series and three partial differential equations with coefficients of Fourier’s series are obtained. The contact force has been considered as a Fourier’s series of impactor displacement and deflection of top face sheet. Also, the model is verified by experiments performed on sandwich panel with epoxy/woven-fiberglass composites, face sheets and polyurethane foam core, and other researchers’ works. The history of contact forces and lateral displacement of contact point has been obtained experimentally and compared with theoretical model. Finally, the effects of impact energy and geometrical parameters including in-plane dimension ratio, core thickness, and face sheet thickness on contact force and lateral deflection histories have been investigated.

Evaluation of the dynamic properties of an aluminum syntactic foam core sandwich

The purpose of this study is to evaluate the dynamic mechanical properties of syntactic foam core sandwich structures. Aluminum matrix syntactic foams with carbon fabric skins are studied. Syntactic foams incorporate porosity in their foam-like structure by means of hollow particles. The material examined here is composed of a core made of aluminum A356 matrix filled with alumina hollow particles. Two types of sandwich composites are studied containing: (a) a single layer of carbon fabric and (b) three layers of the same fabric in 0°/90° orientation. Dynamic characterization was conducted using a free vibration method to determine the resonant frequency of the sandwich beams. The dynamic modulus, storage modulus, loss modulus and damping ratio were calculated from the test results. The experimental results were used to validate the predictions of a theoretical model. The experimental values for Young's modulus of one- and three-layer fabric sandwiches were measured to be 32.57 ± 2.15 and 37.33 ± 1.12 GPa, respectively. The experimental results are in close agreement with the theoretical model.

Determination of mode I & II strain energy release rates in composite foam core sandwiches. An experimental study of the composite foam core interfacial fracture resistance

Abstract The use of composite materials is on the rise in different engineering fields. Following this trend the wind turbine industry has adopted composites as their primary material of choice. For wind turbine blades having large unsupported functional aerodynamic surfaces; the structural stiffness is very important. Stiffness is required to keep the deformations to a minimum under aerodynamic forces. The blade is thus stiffened using sandwich structures at high strain locations within the structure. The lightweight foam cored sandwiches though add stiffness, at the same time pose a challenge for design as the difference in stiffness of both the face-plate and the foam core is very high. The resistance to fracture in any part of the structure is an important design parameter to be determined. The determination of fracture resistance quantified here as the Strain Energy Release Rate (SERR) poses some unique challenges when dealing with highly heterogeneous materials in terms of stiffness. In this study some approaches have been analyzed while others are developed to tackle this problem and to measure the Mode I & II SERR of the face-plate foam-core interface. The sandwich core varies in both thickness and density depending on the loading and thus the location along the blade length. However for this study we have used a single density of foam core for the most part of the turbine blade. Different thicknesses of the foam cores are used to determine the effect of scale on the calculated SERR.

Sound transmission loss characteristics of sandwich aircraft panels: Influence of nature of core

Sandwich panel which has a design involving acoustic comfort is always denser and larger in size than the design involving mechanical strength. The respective short come can be solved by exploring the impact of core geometry on sound transmission characteristics of sandwich panels. In this aspect, the present work focuses on the study of influence of core geometry on sound transmission characteristics of sandwich panels which are commonly used as aircraft structures. Numerical investigation has been carried out based on a 2D model with equivalent elastic properties. The present study has found that, for a honeycomb core sandwich panel in due consideration to space constraint, better sound transmission characteristics can be achieved with lower core height. It is observed that, for a honeycomb core sandwich panel, one can select cell size as the parameter to reduce the weight with out affecting the sound transmission loss. Triangular core sandwich panel can be used for low frequency application due to its increased transmission loss. In foam core sandwich panel, it is noticed that the effect of face sheet material on sound transmission loss is significant and this can be controlled by varying the density of foam.